With advances in technology, wireless communications protocols have become more sophisticated and demanding. Specifically, timing requirements related to communications between two wireless devices may be increasingly restrictive. For example, third generation and later cellular communications protocols may have tight restrictions regarding synchronization between a base station and a mobile terminal, such as a cell phone, a personal digital assistant (PDA), or the like.
In a continuous transmit system, such as a Wideband Code Division Multiple Access (WCDMA) system, a mobile terminal may begin a continuous transmission in response to a command from a base station. The start of the continuous transmission may be timed, with tight timing requirements, from the receipt of the command. For example, in a third generation (3G) WCDMA system, the start of the continuous transmission must be timed within +/−1.5 chips relative to a slot boundary of the received command. A chip is a bit in a spreading signal, which is used to encode data bits in a direct sequence spread spectrum system, such as a WCDMA system. Later generation systems may have tighter timing requirements than third generation systems.
Timing errors may be introduced at the start of the continuous transmission due to variable or uncompensated latencies in the mobile terminal. For example, the mobile terminal may include a baseband integrated circuit (IC) and an RF IC that communicate with each other using a baseband communications link. A start transmission command may be received and down-converted by the RF IC, sent to the baseband IC over the baseband communications link, and processed by the baseband IC to create a transmit start command, which is sent to the RF IC over the baseband communications link. The RF IC decodes and executes the transmit start command to begin continuous transmission. However, uncompensated latencies or variances in latencies introduced by the baseband IC, the RF IC, or the baseband communications link may introduce transmit timing errors that cannot be corrected. Thus, there is a need to reduce timing errors at the start of a transmission due to variable or uncompensated latencies in a mobile terminal.